GCN Circular 41680
Subject
EP250903a: LCO candidate counterpart discovery
Event
Date
2025-09-03T18:47:51Z (8 days ago)
Edited On
2025-09-04T13:36:55Z (8 days ago)
From
Andrew Levan at Radboud University <a.levan@astro.ru.nl>
Edited By
Judith Racusin at NASA/GSFC <judith.racusin@nasa.gov> on behalf of Daniele Bjørn Malesani at Cosmic Dawn Center, Niels Bohr Institute <daniele.malesani@nbi.ku.dk>
Via
Web form
A. J. Levan (Radboud and Warwick), J. A. Quirola-Vasquez (Radboud), D. B. Malesani (DAWN/NBI and Radboud), G. Corcoran (UCD), A. Martin-Carrillo (UCD), R. A. J. Eyles-Ferris (Leicester), P. G. Jonker (Radboud), F. E. Bauer (SSI and UTA), and J. Chacón (PUC) report on behalf of a larger collaboration:
UPDATE: this candidate counterpart has been retracted (and the correct afterglow likely identified). See Levan et al. (GCN 41683).
We observed the location of EP250903a (Zhao et al. GCN 41674) with the Sinistro instrument mounted on the 1-m telescopes at the LCO Siding Springs Observatory. 3 x 300 s exposures were obtained in the SDSS r filter at a start time of 14:44:15 UT on 2025-09-03 (~41 minutes post trigger).
Within the WXT and FXT error circles we locate a new source in our stacked r-band image with r~21 mag (AB) calibrated against nearby SkyMapper stars and not corrected by Galactic extinction, at a location of
RA(J2000): 22:36:27.75
DEC(J2000): -49:51:25.6
The error is about 0.5” in each coordinate. We note the transient is offset ~1” from a Legacy survey object with magnitude r= 21.49 mag which has a photometric redshift of 0.24 +/- 0.11. In the legacy images the source appears to extend underneath the new source. Thus, our photometry likely includes some contribution from the host galaxy.